This invention relates to an improved baffle system for separating entrained liquids from a gas stream. The baffle system of this invention is particularly, but not exclusively suitable for removing contaminants from the air of a work area, such as a paint spray booth having a scrubber system.
Baffle systems for separating liquid entrained in a gas stream have been used for many years. For example, baffle systems are conventionally used for separating water from an air stream in a paint application system. Paint overspray is removed from the paint application booth by downdraft air. The floor of the booth is flooded with water or water emulsion. The water and paint overspray are then received through scrubbers generally located in the floor below the paint application booth. The gas scrubber removes paint particles from the air in the paint booth, entraining the paint particles in the liquid. The air stream is then passed through baffles, removing the entrained liquid from the air stream.
A common form of baffle used by the automotive industry in paint application systems, for example, comprise at least two columns of U-shaped rectangular vertical baffles. The baffles each include a web portion and perpendicular flange portions, such that the web portions of the first column of baffles faces the direction of the air flow and the second column of baffles overlaps the baffles in the first column with the flanges extending toward the direction of air flow. The baffle system thus requires the gas stream to flow around the web portions of the first column of baffles into the rectangular U-shaped baffles of the second column of baffles and around the flange portions of the second column of baffles, depositing the liquid on the baffles which flows downwardly and out of the system. The particle size of the liquid droplets or particles is generally greater than about twenty microns (20xcexc). In a conventional baffle system of this type, the width of the web portion is eight inches, the length of the flange portions are four inches and the flange portions overlap 0.25 inches. The average face velocity measured parallel to the duct in a baffle system for a paint application system of this type is generally between one hundred fifty to three hundred fifty feet per minute (fpm). The problems with this baffle system include re-entrainment and difficulty cleaning.
Various attempts have been made to improve the efficiency of baffle systems for removing entrained liquid from a gas stream. For example, the velocity of the gas stream through the baffle system may be increased by overlapping the ends of the flange portions, thereby improving the efficiency of the baffle system. However, a liquid having entrained paint particles will collect between the overlapping flanges requiring more frequent maintenance. It is also more difficult to clean between the overlapping flanges. More importantly, overlapping flanges provide no improvement in the re-entrainment performance of the baffles. Other proposed attempts to improve the efficiency of baffle systems for removing entrained liquid from a gas stream include complex baffle systems including, for example, spiral baffles, baffles having hook-shapes which further increase the velocity of the gas stream through the baffles to improve efficiency, etc. However, such complex baffle systems are relatively expensive to manufacture and require frequent maintenance particularly where a tacky substance, such as paint, is entrained in the liquid droplets or particles. Such complex baffle systems have not been found suitable for removing liquid entrained in a gas stream in a paint application system.
Thus, there remains a long-felt need for an improved baffle system which is relatively simple in construction, low in cost and having improved efficiency. Further, there is a need to reduce the maintenance costs of conventional baffle systems which reduces the collection of liquid and entrained tacky particles and which is easily cleaned, if necessary. As described below, the improved baffle system of this invention is relatively simple in construction, having reduced costs, particularly when compared to the complex baffle systems described above, and the baffle system of this invention has reduced maintenance costs when compared to baffle systems having overlapping elements.
This application discloses further improvements made to the baffle system of this invention which improves efficiency by reducing re-entrainment of liquid into the gas stream and improves cleaning of accumulation of contaminants on the baffle system during periodic cleaning of the baffle system of this invention.
As set forth above, the baffle system of this invention may be utilized in a paint spray booth wherein the water, air and paint overspray is received through a scrubber or scrubbers located in the floor beneath the paint spray booth. The scrubber removes the paint particles from the air in the paint spray booth and entrains the paint particles in the liquid. The liquid received from the scrubbers is then received in a tank or trough located below the scrubber as disclosed, for example, in U.S. Pat. Nos. 5,100,442 and 6,228,154 assigned to the assignee of the present application. The air is then received through a plurality of baffles where the entrained liquid and paint particles are removed. As will be understood, the efficiency of the baffle system in removing the liquid and entrained particles is critical to the efficiency of the overall system. The baffle system of this invention may also be utilized to separate entrained liquid from a gas stream in other applications.
The baffle system of this invention includes a first column of spaced aligned generally U-shaped baffle members each having a web portion and flange portions extending away from the direction of gas flow and a second column of spaced aligned generally U-shaped baffle members each having a web portion overlapping a web portion of the first column of baffle members and flange portions extending toward the web portions of the first column, such that the baffle members of each column overlap the adjacent column. The gas flowing through the columns of baffles is thus required to take a tortuous path between the baffles and deposits the liquid on the baffles. In the preferred embodiment, the baffles are suspended vertically and the liquid then flows down the baffles into a tank or trough for further processing. In the preferred embodiment of the baffle system, the flange portions extend generally perpendicular to the web portions from the opposed ends of the web portions and the web portions have a width at least three times the length of the flanges as disclosed in the above-referenced parent application.
The improvements to the baffle system disclosed in this application include (1) extending a portion of at least the first column of baffles into the tank or trough which receives the liquid, (2) providing flashing plates at the upper extent of the baffles in contact with the web portions of the coplanar baffle members, wherein the flashing plate on the first column at the upstream side of the baffle assembly has a greater vertical length than the flashing plate on the second column of baffles at the downstream side, (3) utilizing a vertical inlet baffle plate spaced upstream of the baffle members extending into the tank, wherein the upper end has a height of at least 30% of the effective height of the baffle members, and (4) spacing the flange portions of the baffle members of the first and second columns of baffle members a distance of 0.3 to 0.6 inches. As will be understood, these improvements may be utilized individually in the baffle system of this invention. However, it has been found that the greatest improvement in collection efficiency results from using these improvements in combination.
One problem addressed by the improved baffle system of this invention is xe2x80x9cre-entrainmentxe2x80x9d of water droplets on the baffles. As set forth above, the purpose of a baffle system is to remove liquid droplets suspended in a gas stream. The gas stream containing the entrained liquid droplets is directed through the baffle array. The droplets accumulate on the baffles until a liquid film is formed. This liquid film then flows down under the influence of gravity. Ideally, this accumulated liquid flows to the bottom edge of the baffles and runs into a collection system which generally is a tank or trough. As used herein, the term xe2x80x9ctankxe2x80x9d is intended to cover any pool of liquid located beneath the baffle system, whether or not the tank includes an outlet and is thus technically a trough. As will be understood, re-entrainment of the liquid droplets or film into the air stream defeats the purpose of the baffle system and results in water droplets being re-entrained into the dry air stream which is conventionally vented to atmosphere. In a paint application booth, for example, this can result in increased maintenance requirements for the spray booth and possibly undesirable emissions. Further, where the entrained liquid includes contaminants, such as paint particles received in the wash water from a paint spray booth, the baffle system is subject to fouling by waste or oversprayed paint. Normally, the baffle system and the entire tank is cleaned by high pressure washing, generally semi-annually. This problem was partially solved by spacing the columns or arrays of baffles, such that the flange portions did not overlap. However, fouling still occurs on the inside surfaces of the flange portions of the baffles and it is difficult to clean these areas and there is no line of sight between the baffle members unless the baffles are spaced to confirm that the baffles are cleaned. However, spacing the columns of baffles reduces the overall efficiency of the baffle system, but the baffle system of this invention optimizes the spacing to permit cleaning without a significant loss of efficiency. As set forth above, the present invention addresses these problems to provide improved efficiency and cleanability.
In a conventional baffle system, the baffles are spaced above the liquid or water in the tank located below the scrubber generally a distance between one inch and one foot. Thus, the air stream can flow upwardly into the baffle system, reducing the overall efficiency of the system. It has now been found that the efficiency of the baffle system of this invention is improved by extending at least a portion of the xe2x80x9cwet sidexe2x80x9d column of baffles into the tank below the level of the liquid in the tank. As used herein, the term xe2x80x9cwet sidexe2x80x9d refers to the first column of baffles at the upstream side of the baffle system which initially receives the gas stream with the entrained liquid. The term xe2x80x9cdry sidexe2x80x9d refers to the second column of baffles at the downstream side of the baffle system. Of course, where the baffle system includes three or more columns of baffles, the xe2x80x9cdry sidexe2x80x9d of the baffle system will be the last column of baffles at the downstream side of the baffle system. Where a baffle plate is utilized to block the flow of air and entrained liquid upwardly into the baffle system, the plate preferably contacts the web portions of the first column of baffles at the wet side of the baffle system and extends into the collection tank below the level of water in the tank. In the preferred embodiment, however, the first column of baffles at the wet side extends into the liquid receiving tank, such that liquid flowing through the channels is received directly in the tank and the air cannot flow upwardly into the baffles. In the most preferred embodiment, the lower ends of both the first and second column of baffles extends into the tank below the liquid level providing the greatest improvement in efficiency.
Another improvement in efficiency provided by the baffle system of this invention is providing flashing at the top of the baffle system. The baffle array is normally suspended vertically by a bracket attached to the ceiling of the scrubber tank chamber located beneath the paint spray booth. Even in an ideal installation, water droplets collect on the lower surface of the bracket and the moisture then accumulates on the second column of baffles on the downstream or dry side of the baffle system, where the moisture is re-entrained in the airflow through the baffles. The baffle system of this invention prevents this moisture collected on the bracket from reaching the second column and thereby results in improved collection efficiency. The baffle system of this invention includes a flashing system comprising a flashing plate at both the dry and wet sides of the columns of baffle members at the top of the baffles, wherein the flashing on the wet side of the first column of baffle members has a greater vertical length than the flashing on the dry side. In the preferred embodiment, the vertical length of the flashing plate on the wet side or the first column of baffle members is at least three times the vertical length of the flashing plate on the dry side or preferably between three and 10 times the vertical length of the flashing plate on the dry side. Experimentation has established that the greatest efficiency is achieved by providing a flashing plate contacting the web portions of the first column of baffle members having a vertical length of between two inches to 12 inches, preferably between four and eight inches and most preferably about six inches. The flashing contacting the web portions on the second column of baffle members or dry side preferably has a vertical length between one-half inch and three inches. Although the improvement in efficiency provided by the flashing plates is not fully understood, experimentation has established that the greatest efficiency is provided by a flashing plate on the wet side of the first column of baffle members should have a length of about six inches and the flashing plate on the dry side should have a vertical length of at least one-half inch and may have a vertical length of up to about three inches. The lower edge of the dry side flashing plate may be straight or more preferably may include a plurality of angled edges, wherein moisture that collects on the lower edge of the dry side flashing plate runs off onto the baffles. In the most preferred embodiment, the lower angled edges of the dry side flashing plate include a plurality of relatively sharp edges formed by a vertical surface and an angled surface intersecting the vertical surface promoting runoff of the moisture collected on the bottom edge onto the baffles. The angled surface can be any angle which is not horizontal and a 45 degree angle has been found to work well.
It has also been found that a further improvement in liquid collection efficiency of a baffle system of the type disclosed herein is provided by directing the inlet air upwardly at a relatively sharp angle into the column of baffles. This is because the lower portions of the baffles have the greater volume of liquid, but the velocity of air flowing through the baffle system is greater in the lower portion in a conventional baffle system, resulting in re-entrainment of liquid in the gas stream. In the present invention, the air stream is directed upwardly by an inlet or trough baffle spaced from the first and second baffles having a lower end in the tank and an upper end including a flange portion extending toward the inlet stream as is known in the prior art. However, experimentation with the height of the inlet baffle has established that a significant improvement in efficiency can be achieved by raising the inlet or trough baffle to direct the incoming gas upwardly at a steeper angle. In a conventional baffle system, the dry side baffle column is attached to a floor section which forms the downstream side of the tank and which blocks the flow of gas through the bottom of the baffles. Thus, the xe2x80x9ceffective heightxe2x80x9d of the inlet or trough baffle is measured from the top of the floor section to which the dry side baffles are attached. In a baffle system having a vertical length of 6xe2x80x26xe2x80x3 or 78xe2x80x3, the inlet baffle normally extends about 17xe2x80x3 above the floor section to which the dry side baffles are attached or about 20% of the height of the baffles measured from the top of the floor section. However, experimentation has established that by extending the inlet baffle at least 30% or more preferably about 35% of the effective height of the baffles measured from the top of the floor section results in a significant improvement in the efficiency of the baffle system. Again, the reason for this significant improvement is not fully understood, but it is believed that the improvement results from directing the gas stream upwardly at a steeper angle into the baffle columns thereby reducing the velocity of the air stream in the lower portion of the baffles.
Finally, as set forth above, spacing the columns of baffles sufficiently to permit visualization and cleaning of the inside surfaces of the flange portions does not materially reduce the efficiency of the baffle system, provided the spacing is relatively small. In the preferred embodiment, the baffle system comprises a plurality of spaced generally U-shaped baffle members, wherein each baffle member includes a web portion and a flange portion extending generally perpendicular from the opposed sides of the web portion including a first column of baffle members having flange portions extending away from the direction of flow of the gas stream and a second adjacent column of baffle members each having a flange portion extending toward the web portions of the first column in overlapping relation. As set forth in the above-referenced parent application, it has been found that a significant improvement in efficiency results from dimensioning the baffle members wherein the width of the web portions of the baffle members is equal to or greater than three times the length of the flange portions and the flange portions of the columns of baffle members do not overlap. However, as set forth above, experimentation has now established that the flange portions of the adjacent columns may be spaced a distance of between 0.3 and 0.6 inches without a material loss of efficiency. This spacing, however, permits cleaning and visualization of the flange portions between the columns, thereby assuring complete cleaning of the baffle members and therefore improved efficiency.
Other advantages and meritorious features of the baffle system of this invention will be more fully understood from the following description of the preferred embodiments, the appended claims and the drawings, a brief description of which follows.